A brake unit of this type is shown in U.S. Pat. No. 3,995,537 and has been commercially successful for a great number of years. In order to further improve this brake unit, development work has been performed. A major goal with this work has been to improve the internal guiding, which in the known unit is performed by sliding friction between a common slack adjuster tube and the housing at two places, and to reduce the mechanical hysteris of the unit.